G proteins in tumor growth and angiogenesis

ABSTRACT

The invention provides an agent that reduces the expression of Gα12 or Gα13 polypeptide, as well as an agent that enhances G protein Gα12 or Gα13 expression and/or activity. An agent of the invention may be used to decrease or increase G protein Gα12 or Gα13 expression and/or activity thereby to treat or prevent the onset of a disease or condition associated with Gα12 or Gα13 expression and/or activity. The invention also provides a method for screening for an anti-cancer or anti-angiogenesis agent, as well as an agent that promotes angiogenesis.

RELATED APPLICATION

This application claims priority of U.S. provisional application Ser. No. 60/808,489, filed May 25, 2006, which is herein incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Work relating to this application was supported by a grant from the U.S. Government (RO1 GM56904). The government may have certain rights in the invention.

TECHNICAL FIELD

The invention relates to G protein and its involvement in angiogenesis.

BACKGROUND

Blood vessels are crucial for organ growth in the embryo and repair of wounded tissue in the adult. An imbalance in the growth of blood vessels contributes to the pathogenesis of numerous disorders including malignant, ocular and inflammatory disorders. Carmeliet, Nature 438: 932-936 (2005). Excessive or abnormal angiogenesis may contribute to conditions such as obesity, asthma, diabetes, cirrhosis, multiple sclerosis, endometriosis, AIDS, bacterial infections and autoimmune disease. Id. Insufficient angiogenesis may cause endothelial cell dysfunction and vessel malformation or regression; it may also prevent revascularization, healing and regeneration thereby contributing to ischaemic heart disease or preeclampsia. Id. To date, it has been reported that in Western nations, at least 184 million patients could benefit from some form of anti-angiogenesis therapy, while at least 314 million patients would benefit from some form of angiogenesis-stimulating therapy (http://www.angio.org/understanding/content_understanding.html (last retrieved May 16, 2006)).

Although a great deal of effort has been undertaken to develop therapies to promote revascularization of ischemic tissue or to inhibit angiogenesis in cancer and ocular, joint or skin disorders, toxicities and acquired resistance associated with currently available therapeutics indicate that continued efforts to develop novel strategies for treating angiogenesis-associated conditions are needed.

SUMMARY OF THE INVENTION

The present invention involves the discovery that a reduction of the expression and/or activity the α subunit of an heterotrimeric GDP/GTP-binding protein that functions as a cellular signal transducer, herein “G protein,” results in a reduction of tumor growth as well as angiogenesis. Thus, the invention provides angiogenesis-modulating agents that can reduce the expression of a G protein, as well as cells and compositions that contain one or more agents that can reduce or enhance the expression and/or activity of a G protein. The invention also provides methods for reducing or increasing expression and/or activity of a G protein, methods for reducing angiogenesis, and methods for promoting angiogenesis in a mammal. In addition, the invention provides methods of screening for anti-angiogenesis and anti-cancer agents, as well as methods of screening for agents that promote angiogenesis.

The invention provides an oligonucleotide that is capable of hybridizing to a nucleic acid encoding a Gα₁₂ or Gα₁₃ polypeptide under intracellular conditions and reducing expression of the nucleic acid in a cell. In some embodiments, the oligonucleotide hybridizes under intracellular conditions to a nucleic acid comprising a sequence that encodes a polypeptide having the sequence of SEQ ID NO: 2 or 4 or a polypeptide having a sequence substantially homologous to SEQ ID NO: 2 or 4. In some embodiments, the oligonucleotide hybridizes under intracellular conditions to a nucleic acid comprising SEQ ID NO: 1, 3, and/or the complement of SEQ ID NO: 1 or 3. Thus, in some embodiments, the nucleic acid encoding the Gα₁₂ or Gα₁₃ polypeptide comprises SEQ ID NO: 1 or 3, or the Gα₁₂ or Gα₁₃ polypeptide comprises SEQ ID NO: 2 or 4.

In some embodiments, the oligonucleotide is an antisense molecule capable of hybridizing to a nucleic acid encoding the Gα₁₂ or Gα₁₃ polypeptide under intracellular conditions. In one embodiment, the antisense molecule has a sequence that is identical to 17 to 33 contiguous nucleotides of SEQ ID NO: 1, 3, or the complement of SEQ ID NO: 1 or 3. In one embodiment, the antisense molecule consists of 17 to 33 contiguous nucleotides of the complement of SEQ ID NO: 1 or 3. In another embodiment, the antisense molecule has the sequence of any of SEQ ID NO: 6-9 and 11-145, or their complement. The antisense molecule may consists of the sequence of any of SEQ ID NO: 6-9 and 11-145.

In some embodiments, the oligonucleotide includes one or more ribose nucleotides, deoxyribose nucleotides, modified nucleotides, or any combinations thereof.

The invention also provides an expression vector comprising an expression control sequence that is capable of directing production of an oligonucleotide, the nucleotides of which are ribose nucleotides. In some embodiments, the expression control sequence directs production of a ribose nucleic acid transcript that hybridizes under intracellular conditions to SEQ ID NO: 1, 3 and/or to the complement of SEQ ID NO: 1 or 3.

The invention also provides a cell comprising a guanine diphosphate analogue, a guanine triphosphate analogue, an oligonucleotide capable of reducing expression of a nucleic acid encoding a Gα₁₂ or Gα₁₃ polypeptide, or any combination thereof. In some embodiments, the analogue is GTP gamma S, GDP beta S, GppNHp, or GppCH2p; and/or the oligonucleotide has the sequence of SEQ ID NO: 6-9.

The invention also provides a method for producing a cell that has a guanine diphosphate analogue, a guanine triphosphate analogue, an oligonucleotide capable of reducing expression of a nucleic acid encoding a Gα₁₂ or Gα₁₃ polypeptide, or any combination thereof. The method involves contacting the cell with a guanine diphosphate analogue, a guanine triphosphate analogue, an oligonucleotide capable of reducing expression of a nucleic acid encoding a Gα₁₂ or Gα₁₃ polypeptide, or any combination thereof.

The invention also provides a composition comprising a pharmaceutically acceptable carrier and a therapeutically effective amount of an agent that reduces the expression and/or activity of Gα₁₂ or Gα₁₃. In some embodiments, the agent is a guanine diphosphate analogue, a guanine triphosphate analogue, an oligonucleotide capable of reducing expression of a nucleic acid encoding a Gα₁₂ or Gα₁₃ polypeptide, or any combination thereof.

The invention also provides a method for modulating angiogenesis in a mammal that involves modulating the expression and/or activity of Gα₁₂ or Gα₁₃ in a cell of the mammal. The method involves administering a guanine diphosphate analogue, a guanine triphosphate analogue, an inhibitory antibody or biologically active fragment thereof that binds specifically to the carboxy-terminal region of the Gα₁₂ or Gα₁₃ polypeptide, an oligonucleotide capable of reducing expression of a nucleic acid encoding a Gα₁₂ or Gα₁₃ polypeptide, or any combination thereof, in an amount effective to decrease expression and/or activity of the Gα₁₂ or Gα₁₃ polypeptide. In some embodiments, the analogue administered is GDP beta S, GppNHp, and GppCH2p; and/or the oligonucleotide administered has the sequence of SEQ ID NO: 6-9. In some embodiments, the analogue, oligonucleotide, inhibitory antibody or biologically-active fragment thereof, or any combination thereof, is administered by direct injection to a localized area.

In some embodiments, the expression and/or activity of Gα₁₂ or Gα₁₃ is decreased by about 20% to about 90%. In some embodiments, the expression and/or activity of Gα₁₂ or Gα₁₃ is decreased by about 30% to about 70%. In some embodiments, the mammal has cancer. Thus, the invention also provides a method for reducing tumor growth or growth of a cancer cell in a mammal that involves reducing the expression and/or activity of a Gα₁₂ or Gα₁₃ in the mammal. The mammal may have melanoma, lung cancer or lymphoma.

In some embodiments, methods for modulating angiogenesis in a mammal involve increasing the expression and/or activity of Gα₁₂ or Gα₁₃ in the mammal such that angiogenesis is promoted. In one embodiment, the method involves administering to the mammal a composition comprising GTP gamma S in an amount effective to increase activity of the Gα₁₂ or Gα₁₃ polypeptide. In one embodiment, the method involves administering an expression vector comprising an expression control sequence that directs production of a nucleic acid encoding a Gα₁₂ or Gα₁₃ polypeptide

The invention also provides a method of screening for an angiogenesis-modulating agent that involves contacting a cell expressing Gα₁₂ or Gα₁₃ with a candidate compound, determining whether the expression and/or activity of Gα₁₂ or Gα₁₃ is reduced or increased in the cell, and identifying a candidate compound as an angiogenesis-modulating agent if the candidate compound reduces or increases the expression and/or activity of Gα₁₂ or Gα₁₃.

In some embodiments, the angiogenesis-modulating agent is an anti-angiogenesis agent or an anti-cancer agent that reduces the expression and/or activity of Gα₁₂ or Gα₁₃. In other embodiments, the angiogenesis-modulating agent is an agent that promotes angiogenesis by increasing the expression and/or activity of Gα₁₂ or Gα₁₃.

As used herein, the term “reduce” means a decrease by any amount such as, for example, by 2%, 5%, 10%, 20%, 40% or more than 40%.

As used herein, the term “increase” means an increase by any amount such as, for example, by 2%, 5%, 10%, 20%, 40% or more than 40%.

As used herein, the term “Gα₁₂” refers to a G protein having the polypeptide sequence set out in SEQ ID NO: 2 or a polypeptide having a substantially homologous sequence to SEQ ID NO: 2.

As used herein, the term “Gα₁₃” refers to a G protein having the polypeptide sequence set out in SEQ ID NO: 4 or a polypeptide having a substantially homologous sequence to SEQ ID NO: 4.

As used herein, the term “oligonucleotide” means a polymer of 3 or more ribose or deoxyribose nucleotides, which can be naturally-occurring or modified nucleotides as discussed below. Oligonucleotides include primers for nucleic acid amplification or sequencing, probes for nucleic acid detection, or inhibitory molecules for inhibition of nucleic acid expression such as an antisense molecule (antisense RNA) or a ribozyme as discussed herein.

As used herein, the term “intracellular condition” mean conditions (e.g. temperature, pH, salt concentrations) such as those existing in a cell.

As used herein, the term “nucleic acid” includes DNA molecules such as genomic DNA and cDNA, as well as RNA molecules such as mRNA. It also includes viral DNA and RNA, as well as plasmids, cosmids and other forms of expression systems such as expression cassettes. Nucleic acids may be single stranded or double stranded.

As used herein, the term “complementary” or “complement” refers to a nucleic acid or oligonucleotide that is able to bind, that is hybridize, to another nucleic acid molecule or oligonucleotide through the formation of H-bonds between nucleotides (e.g. A with T or U and G with C) to form a double stranded molecule.

As used herein, the phrase “substantially homologous,” in reference to a polypeptide, means that the polypeptide sequence is largely, though not entirely homologous to another polypeptide, and retains the same functional activity as the second polypeptide. When an amino acid position in two polypeptides is occupied by identical amino acids, then they are homologous at that position. A polypeptide is substantially homologous to another polypeptide if it exhibits at least 70%, preferably 80%, more preferably 90% homology to the second polypeptide. With respect to G proteins, a polypeptide substantially homologous to a G protein will have the four highly conserve domains characteristic of all G proteins shown in FIG. 15. These four highly conserved domains include (a) a first region (open box A) that corresponds to the region in Gα₁₂ or Gα₁₃ having the sequence ILLLGAGESGKSTFLKQ (SEQ ID NO: 147); (b) a second region (open box C) having the sequence DVGGQR (SEQ ID NO: 162); (c) a third region (open box G) having the sequence LFLNKXD (SEQ ID NO: 163) where X is any amino acid; and (d) a fourth region (open box I) that corresponds to the region having the sequence TTAIDT (SEQ ID NO: 151) in Gα₁₂.

As used herein, the phrase “expression vector” means a nucleic acid molecule capable of transporting and/or allowing for the expression of another nucleic acid to which it has been linked. The product of that expression is referred to as a messenger ribose nucleic acid (mRNA) transcript. Thus, expression vectors contain appropriate expression control sequences that may direct expression of a nucleic acid that is operably linked to the expression control sequence to produce a transcript.

As used herein, the phrase “expression control sequence” means a nucleic acid sequence sufficient to direct transcription of another nucleic acid sequence that is operably linked to the expression control sequence to produce an RNA transcript when appropriate molecules such as transcriptional activator proteins are bound the expression control sequence.

As used herein, the term “operably linked” means that a nucleic acid and an expression control sequence is positioned in such a way that the expression control sequence directs expression of the nucleic acid when the appropriate molecules such as transcriptional activator proteins are bound to the expression control sequence.

As used herein, the term “antibody” means an immunoglobulin molecule and immunologically active portions thereof.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. Amino acid designations may include full name, three-letter, or single-letter designations as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Other features and advantages of the invention will be apparent from the following detailed description and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1. Gα₁₃ is required for PDGF-induced cell migration. A. Wound-healing assay showed that PDGF-BB (20 ng/mL) or serum (10% FBS) induced the migration of serum-starved wild-type MEF cells. B. Wound-healing assay showed that serum, but not PDGF, induced the migration of Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Data are representative of five experiments. C. Chamber assay of PDGF and serum-induced wild-type MEF cell migration. D. Chamber assay of PDGF and serum-induced Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cell migration. Results are the mean±s.d. of three independent chambers. E. Deficiency of Gα₁₂ and Gα₁₃ had no effect on PDGF-induced activation of MAPK. Bottom panel: Western blot with anti-ERK MAPK antibody showing that similar amounts of cell lysates were used in each lane. Data are representative of three experiments. F. Wound-healing assay showed that PDGF did not induce the migration of serum-starved Gα₁₂-re-expressing Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells (Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₂ cells). G. Wound-healing assay showed that Gα₁₃ rescued PDGF-induced migration of Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells (Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₃ cells). Data are representative of three experiments. H. Chamber assay of PDGF and serum-induced Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₂ cell migration. I. Chamber assay of PDGF and serum-induced Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₃ cell migration. Results are the mean±s.d. (n=3).

FIG. 2. EGF failed to induce the migration of Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Left panels: wound-healing assay showed that EGF and serum induced the migration of serum-starved wild-type MEF cells. Middle panels: serum, but not EGF, induced the migration of Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Right panels: EGF and serum induced cell migration of the Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells expressing wild-type Gα₁₃. Data are representative of three experiments.

FIG. 3. Deficiency of Gα₁₃ and Gα₁₃ RNAi inhibited PDGF-induced cell migration. A. Wound-healing assays showed that serum, but not PDGF and EGF, induced the migration of Gα₁₃ ^(−/−) cells. Re-expression of either a wild-type Gα₁₃ or a C-terminal truncated Gα₁₃ mutant rescued the migratory response to PDGF or EGF. Data are representative of five experiments. B. Western blots were performed with whole cell extracts prepared from MEF cells, Gα₁₃ ^(−/−) cells, Gα₁₃ ^(−/−)+WT Gα₁₃ cells, and Gα₁₃ ^(−/−)+C-terminal truncated Gα₁₃ cells. The expression levels of WT Gα₁₃ and the C-terminal truncated Gα₁₃ mutant proteins were similar, 80% of endogenous Gα₁₃ protein. C. Western blots were performed with whole cell extracts prepared from MEF cells treated with control siRNA, Gα₁₃ siRNA, or cells transfected with both Gα₁₃ siRNA and wild-type human Gα₁₃. D. Chamber assay of PDGF-induced migration of MEF cells treated with control siRNA, Gα₁₃ siRNA, or cells transfected with both Gα₁₃ siRNA and wild-type human Gα₁₃. Results are the mean±s.d. of three independent chambers. E. Wound-healing assay showed that Gα₁₃ siRNA treatment reduced PDGF-induced MEF cell migration. Data are representative of three experiments.

FIG. 4. RacG12V failed to induce Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cell migration. A. PDGF-induced MEF cell migration was blocked by a dominant-negative mutant Rac (RacT17N). Western blot in the right panel shows the expression levels of Rac proteins in untransfected and transfected cells. B. A constitutive active mutant Rac (Rac1G12V) induced MEF cell migration, while transfection of a control empty vector plasmid or of Gα₁₃QL plasmid did not. The expression levels of Rac and Gα₁₃ proteins in untransfected and transfected cells are shown by western blots (right panels). C. Rac1G12V did not induce Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cell migration. All above data were from wound-healing assays and are representative of three experiments. Western blot (right panel) shows the expression levels of Rac proteins in untransfected and transfected cells. D. Chamber assay of Rac1G12V effect on the migration of MEF and Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Results are mean±s.d. (n=3). The expression levels of Rac proteins in untransfected and transfected cells are shown by western blot (right panel). E. Rac activation assay. Cell lysates from MEF or Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells with or without PDGF treatment were incubated with GST-PBD. The pulled-down active Rac was immunoblotted with anti-Rac antibody. The bottom panel shows the western blot with anti-Rac of the cell lysate used (10% of that used in the top panel). Data are representative of three experiments.

FIG. 5. PDGF-induced Gα₁₃-dependent cell migration does not require GPCR coupling. A. Two models that could explain the role of Gα₁₃ in PDGF-induced cell migration (see text for description). B. LPA-induced actin stress fiber formation in wild-type MEF cells, Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+wild-type (WT) Gα₁₃ cells, and Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+C-terminal truncated Gα₁₃ cells. C. Western blots were performed with whole cell extracts prepared from wild-type MEF cells, Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+wild-type (WT) Gα₁₃ cells, and Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+C-terminal truncated Gα₁₃ cells. The expression levels of WT Gα₁₃ and the C-terminal truncated Gα₁₃ mutant proteins were similar, ˜25% of endogenous Gα₁₃ protein. D. Wound-healing assay of PDGF-induced migration of the Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells expressing a C-terminal truncated Gα₁₃. E. Chamber assay of PDGF-induced migration of Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells expressing a C-terminal truncated Gα₁₃. F. LPA induced the migration of MEF cells and Gα₁₃ ^(−/−)+WT Gα₁₃ cells, but not Gα₁₃ ^(−/−) cells and Gα₁₃ ^(−/−)+C-terminal truncated Gα₁₃ cells. Data are representative of three experiments.

FIG. 6. LPA (10 μM) induced actin stress fiber formation in Gα₁₃ ^(−/−)+wild-type (WT) Gα₁₃ cells, but not in Gα₁₃ ^(−/−) and Gα₁₃ ^(−/−)+C-terminal truncated Gα₁₃ cells. Data are representative of three experiments.

FIG. 7. Rac and G₁₃ form a complex in vitro and in cells. A. Diagram of the Gα₁₃, Gail, and the chimera Gα_(13/i)-DD1 constructs. B. Purified GST-Rac or GST-Rho pre-loaded with GDP or GTPγS was mixed with purified Gα₁₃, Gα_(i1), and Gα_(13/1)-DD1 pre-loaded with GDP or GTPγS. Glutathione-beads were used to pull-down. Western blots were with anti-His₆ antibodies. C. Purified Rac pre-loaded with GTPγS and/or purified wild-type Gα₁₃ pre-loaded with GDP were pulled down with anti-Rac or anti-Rho antibodies. Western blots were with an anti-Gα₁₃ antibody. D. Purified Rac pre-loaded with GTPγS, purified wild-type Gα₁₃ pre-loaded with GDP, and/or purified Gβγ were pulled down with anti-Rac or anti-Gα₁₃ antibodies. Western blots were with an anti-GP antibody. E. HEK293T cells were transfected with indicated plasmids. Whole cell lysates were prepared and immunoprecipitated with anti-Rac antibodies. Western blot was with anti-Gα₁₃ or anti-Gα₁₂ antibody. F. MEF cell lysates were immunoprecipitated with anti-Rac antibody and western blotted with anti-Gα₁₃ antibody. Data are representative of three to five experiments.

FIG. 8. Subcellular localization of Rac. A. Subcellular localization of Rac in MEF cells and in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, without or with PDGF treatment. B. Subcellular localization of cortactin in MEF cells and in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, without or with PDGF treatment. C. Subcellular localization of F-actin polymers in MEF cells and in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, without or with PDGF treatment. Data are representative of three to five experiments.

FIG. 9. Role of Gα₁₃ in tumor angiogenesis. A. Western blots were performed with whole cell extracts prepared from mouse endothelial SVEC4-10 cells treated with control siRNA, Gα₁₃ siRNA, or cells transfected with both Gα₁₃ siRNA and wild-type human Gα₁₃. B. Chamber assay of VEGF-induced migration of mouse endothelial SVEC4-10 cells treated with control siRNA, Gα₁₃ siRNA, or cells transfected with both Gα₁₃ siRNA and wild-type human Gα₁₃. Results are the mean±s.d. of three independent chambers. C. B-16 mouse melanoma tumor growth in Gα₁₃ ^(+/−) mice and wild-type littermates. Each group consisted often mice. D. LLC tumor growth in Gα₁₃ ^(+/−) mice and wild-type littermates. Each group consisted often mice. E. Hematoxylin and eosin staining of tumor xenografts (Left: wild-type littermate and Right: Gα₁₃ ^(+/−)). F. Representative pictures of anti-PECAM staining of sections of tumor xenografts from wild-type littermates (Left) or from Gα₁₃ ^(+/−) mice (Right). G. Representative pictures of anti-VEGFR2 staining of sections of tumor xenografts from wild-type littermates (Left) or from Gα₁₃ ^(+/−) mice (Right).

FIG. 10 is a graph illustrating the importance of Gα₁₂ in tumor growth.

FIG. 11A-B depict the nucleic acid sequence of G protein Gα₁₂ (NM_(—)007353).

FIG. 12 is the amino acid sequence of G protein Gα₁₂.

FIG. 13A-B depict the nucleic acid sequence of G protein Gα₁₃ (NM_(—)006572).

FIG. 14 is the amino acid sequence of G protein Gα₁₃.

FIG. 15 is a schematic diagram illustrating the various domains in the α subunit of an heterotrimeric GDP/GTP-binding protein. Regions of highest amino acid sequence diversity are indicated by hatched boxes. Regions of highly conserved domains found in all G proteins and thought to be directly involved in interaction with the guanine nucleotide are indicated by clear boxes (A, C, G, and I). The single letter amino acid code is used to show the distinctive sequences for some of the Gα subunits. See Simon et al., Science 252:802 (1991).

DETAILED DESCRIPTION

The present invention involves the discovery that a reduction of the expression and/or activity of the α subunit of an heterotrimeric GDP/GTP-binding protein that functions as a cellular signal transducer, herein “G protein,” results in a reduction of angiogenesis and tumor growth. More specifically, the invention is based on the discovery that xenografted tumors failed to grow in Gα₁₃ ^(+/−) and in Gα₁₂ ^(−/−) mice, as well as the discovery that Gα₁₃ ^(+/−) mice showed impaired tumor vascularization. Thus, the invention provides angiogenesis-modulating agents that reduce the expression and/or activity of a G protein, as well as agents that increase their expression and/or activity. The invention also provides methods for reducing or increasing expression and/or activity of a G protein, methods for reducing angiogenesis and/or tumor growth in a mammal, and methods for promoting angiogenesis in a mammal. In addition, the invention provides methods of screening for anti-angiogenesis and anti-cancer agents, as well as methods of screening for agents that promote angiogenesis.

Agents of the Invention

The invention provides an angiogenesis-modulating agent that can reduce or increase expression and/or activity of a G protein. As used herein, the term “G protein” refers to the α subunit of an heterotrimeric GDP/GTP-binding protein having α, β and γ subunits that functions as a cellular signal transducer. Heterotrimeric GDP/GTP-binding proteins relay signals from transmembrane receptors such as G protein-coupled receptors (GPCRs) to downstream effectors. More specifically, interaction of a heterotrimeric GDP/GTP binding protein with its ligand-activated receptor promotes exchange of a guanosine diphosphate (GDP), bound to the α subunit, for guanosine triphosphate (GTP) and the subsequent dissociation of the α-GTP complex from the βγ heterodimer. A G protein may be from any source, for example, from a mouse, a rabbit, a pig, a dog, a cow, a monkey, or a human. A G protein may be identified based on sequence and function. Simon et al., Science 252:802 (1991). For example, a G protein has the four highly conserved domains as illustrated in FIG. 15 (SEQ ID NO: 146-163). G proteins may also be grouped into families, e.g. G_(s), G_(i), G_(q) and G₁₂, based on their amino acid sequences. See, for example, Simon et al., Science 252:802 (1991). Examples of G proteins of the invention include Gα₁₂ and Gα₁₃, as well as any polypeptide that is substantially homologous to Gα₁₂ or Gα₁₃, that is, it has the four highly conserved domains characteristic of G proteins illustrated in FIG. 15 and at least 70% amino acid sequence homology with Gα₁₂ or Gα₁₃. The term “G protein” also includes any biologically active fragment of the full-length polypeptide.

An agent that can reduce or increase the expression and/or activity of a G protein may decrease or increase its expression and/or activity by any amount such as, for example, by 2%, 5%, 10%, 20%, 40% or more than 40%.

In one embodiment, an agent of the invention may be an oligonucleotide that will hybridize to a G protein nucleic acid under intracellular or stringent conditions. The oligonucleotide is capable of reducing expression of a nucleic acid encoding the G protein. A nucleic acid encoding a G protein may be genomic DNA as well as messenger RNA. It may be incorporated into a plasmid vector or viral DNA. It may be single strand or double strand, circular or linear. Examples of nucleic acids encoding G proteins are set forth in SEQ ID NO. 1 and 3. See FIGS. 11A-B and 13A-B. G protein nucleic acids may also be a fragment of the sequences set forth in SEQ ID NO: 1 and 3 provided that the nucleic acids encode a biologically active polypeptide.

An oligonucleotide is a polymer of ribose nucleotides or deoxyribose nucleotides having more than 3 nucleotides in length. An oligonucleotide may include naturally-occurring nucleotides; synthetic, modified, or pseudo-nucleotides such as phosphorothiolates; as well as nucleotides having a detectable label such as P³², biotin or digoxigenin. An oligonucleotide that can reduce the expression and/or activity of a G protein nucleic acid, that is an oligonucleotide of the invention, may be completely complementary to the G protein nucleic acid. Alternatively, some variability between the sequences may be permitted. An oligonucleotide that can hybridize to a G protein nucleic acid under intracellular conditions or under stringent hybridization conditions, is sufficiently complementary to inhibit expression of a G protein nucleic acid. Intracellular conditions refer to conditions such as temperature, pH and salt concentrations typically found inside a cell, e.g. a mammalian cell. One example of such a mammalian cell is the MEF cell described below or an endothelial, smooth muscle or neuronal cell. Generally, stringent hybridization conditions are selected to be about 5° C. lower than the thermal melting point (T_(m)) for the specific sequence at a defined ionic strength and pH. However, stringent conditions encompass temperatures in the range of about 1° C. to about 20° C. lower than the thermal melting point of the selected sequence, depending upon the desired degree of stringency as otherwise qualified herein. Inhibitory oligonucleotides that comprise, for example, 2, 3, 4, or 5 or more stretches of contiguous nucleotides that are precisely complementary to a G protein coding sequence, each separated by a stretch of contiguous nucleotides that are not complementary to adjacent coding sequences, may inhibit the function of a G protein nucleic acid. In general, each stretch of contiguous nucleotides is at least 4, 5, 6, 7, or 8 or more nucleotides in length. Non-complementary intervening sequences may be 1, 2, 3, or 4 nucleotides in length. One skilled in the art can easily use the calculated melting point of an oligonucleotide hybridized to a sense nucleic acid to estimate the degree of mismatching that will be tolerated for inhibiting expression of a particular target nucleic acid. Oligonucleotides of the invention include, for example, a ribozyme or an antisense nucleic acid molecules.

The antisense nucleic acid molecule may be single or double stranded (e.g. a small interfering RNA (siRNA)), and may function in an enzyme-dependent manner or by steric blocking. Antisense molecules that function in an enzyme-dependent manner include forms dependent on RNase H activity to degrade target mRNA. These include single-stranded DNA, RNA, and phosphorothioate molecules, as well as the double-stranded RNAi/siRNA system that involves target mRNA recognition through sense-antisense strand pairing followed by degradation of the target mRNA by the RNA-induced silencing complex. Steric blocking antisense, which are RNase-H independent, interferes with gene expression or other mRNA-dependent cellular processes by binding to a target mRNA and getting in the way of other processes. Steric blocking antisense includes 2′-O alkyl (usually in chimeras with RNase-H dependent antisense), peptide nucleic acid (PNA), locked nucleic acid (LNA) and morpholino antisense.

Small interfering RNAs, for example, may be used to specifically reduce G protein translation such that the level of G protein polypeptide is reduced. SiRNAs mediate post-transcriptional gene silencing in a sequence-specific manner. See, for example, http://www.ambion.com/techlib/hottopics/rnai/rnai_may2002_print.html (last retrieved May 10, 2006). Once incorporated into an RNA-induced silencing complex, siRNA mediate cleavage of the homologous endogenous mRNA transcript by guiding the complex to the homologous mRNA transcript, which is then cleaved by the complex. The siRNA may be homologous to any region of the G protein mRNA transcript. The region of homology may be 30 nucleotides or less in length, preferable less than 25 nucleotides, and more preferably about 21 to 23 nucleotides in length. SiRNA is typically double stranded and may have two-nucleotide 3′ overhangs, for example, 3′ overhanging UU dinucleotides. Methods for designing siRNAs are known to those skilled in the art. See, for example, Elbashir et al. Nature 411: 494-498 (2001); Harborth et al. Antisense Nucleic Acid Drug Dev. 13: 83-106 (2003). Typically, a target site that begin with AA, have 3′ UU overhangs for both the sense and antisense siRNA strands, and have an approximate 50% G/C content is selected. SiRNAs may be chemically synthesized, created by in vitro transcription, or expressed from an siRNA expression vector or a PCR expression cassette. See, e.g., http://www.ambion.com/techlib/tb/tb_(—)506html (last retrieved May 10, 2006). When an siRNA is expressed from an expression vector or a PCR expression cassette, the insert encoding the siRNA may be expressed as an RNA transcript that folds into an siRNA hairpin. Thus, the RNA transcript may include a sense siRNA sequence that is linked to its reverse complementary antisense siRNA sequence by a spacer sequence that forms the loop of the hairpin as well as a string of U's at the 3′ end. The loop of the hairpin may be of any appropriate lengths, for example, 3 to 30 nucleotides in length, preferably, 3 to 23 nucleotides in length, and may be of various nucleotide sequences including, AUG, CCC, UUCG, CCACC, CTCGAG, AAGCUU, CCACACC and UUCAAGAGA (SEQ ID NO: 10). SiRNAs also may be produced in vivo by cleavage of double-stranded RNA introduced directly or via a transgene or virus. Amplification by an RNA-dependent RNA polymerase may occur in some organisms.

Examples of siRNA sequences that can hybridize to a G protein Gα₁₂ nucleic acid include the following sequences and their complementary sequences:

SEQ ID NO. Pos siRNA Sequence 11 3491 AAGCAUGAGAGGAAGGAGAUAUU 12 789 AAGGGAAUUGUGGAGCAUGACUU 13 1479 AAGGACAUGGAAACUGUCACGUU 14 1573 AAUCACACAGCUUGCUUUGCUUU 15 4242 AAUGGUAGUGGUCCGGGUCAGUU 16 2224 AAGUCAUCUGCUCACACACAGUU 17 1758 AAAGCUUUGCCUAACAGUAGCUU 18 2874 AAACCCGGUAAACGCAAGCCCUU 19 4333 CAGCCUCUGAAUGUUUAUUAAAA 20 665 CAGCCGGAGAAGCGAGUUUCAGC 21 3004 GAGGCUGUGUGUCAGUGUUUGCU 22 723 GACCGGAUCGGCCAGCUGAAUUA 23 3877 GAGGUAGUUGUGCCUCAAUUAUU 24 2340 CAGCUGCUUGGCGAGCUAACAGC 25 365 GAGCGGCAAGUCCACGUUCCUCA 26 1660 UACACACGCUCUGUCUUUAAUGA 27 470 CAAGGGCUCAAGGGUUCUUGUUG 28 626 GAGCGCACUCUGGAGGGAUUCUG 29 1217 CACCGCCAUCGACACCGAGAACG 30 3229 GAGCGUGGUGAGCUUUGUUUGCC 31 2559 GAGCCUGUGAAUGUUGAUACGAG 32 4226 CAGAGGCUCCCAUUGGAAUGGUA 33 4039 GAGUCAUAGGUCUGUAAUUUAUA 34 801 GAGCAUGACUUCGUUAUUAAGAA 35 3874 CAGGAGGUAGUUGUGCCUCAAUU 36 1633 GAGGACCGUGUUGUGUGUGUAUG 37 2167 CAACGGCAAAGACACAGAAACCA 38 1454 CAGCCAGCCAGCGAGCUCUAGGC 39 966 AACCGGCUGGUGGAGUCCAUGAA 40 1636 GACCGUGUUGUGUGUGUAUGUGU 41 4276 AAGCUUUGCACAGUGUAUUAACA 42 275 GAGGCGUAGCCGCGACAUCGACG 43 2002 CAGGUGUGGAUUCACCUUACGCC 44 1662 CACACGCUCUGUCUUUAAUGACA 45 2249 CAGCACAUAGCGUUUCCUUCUUU 46 2382 CAGACGCUGGAGGAAUCUUGAGU 47 3297 GAGCCCAGAGGAAGUGCAAGCGG 48 3494 CAUGAGAGGAAGGAGAUAUUGUG 49 1080 AAGACCGUGAGCAUCAAGAAGCA 50 1194 AAGCCACUCUUCCACCACUUCAC 51 735 CAGCUGAAUUACUUUCCUAGUAA 52 3111 GACCGGAGAUGAGUGCCGAUGAC 53 4275 UAAGCUUUGCACAGUGUAUUAAC 54 2151 CACCCACUGCCCAACCCAACGGC 55 864 CAGCGCCAGAAGUGGUUCCAGUG 56 1795 CACGCCGAUGCUGCUAAACUCAG 57 2168 AACGGCAAAGACACAGAAACCAG 58 3417 UAGUCCGGCCUUGUCAAUGAGUG 59 996 GAGACCAUCGUCAACAACAAGCU 60 1994 GAGCUCUGCAGGUGUGGAUUCAC 61 2058 CAUGCCCAGCAGCACAACACGGA 62 896 GAUCACGUCCAUCCUGUUCAUGG 63 1079 GAAGACCGUGAGCAUCAAGAAGC 64 3295 CAGAGCCCAGAGGAAGUGCAAGC 65 780 AAAGCCACCAAGGGAAUUGUGGA 66 3605 GAGGCACUUGGCCUUGCUGAGCU 67 3933 GAUCUGUUCCUCAUAGCUAUACU 68 4221 UAAGGCAGAGGCUCCCAUUGGAA

Examples of siRNA that can hybridize to a G protein Gα₁₃ nucleic acid include the following sequences and their complementary sequences:

SEQ ID No. Pos siRNA Sequence 69 4629 AAGGCUAAAUAUCAGUGUUAAUU 70 602 AACUUGGAGAACCAGAUUAUAUU 71 4302 AAUACCAUAUGUCCUUAUCAUUU 72 2004 AAGCAACUUGGUAACAGAACUUU 73 3206 AAAGAGGACACUUCAUCUUACUU 74 2102 AAUCCUUACUGUAGGAAAUCAUU 75 665 AAGGCAUCCAUGAAUACGACUUU 76 3387 AAUGUCUCAGAAUCAACAUUCUU 77 3327 AAACACCAAAUAGAUAUCAUGUU 78 741 AAGGAAACGUUGGUUUGAAUGUU 79 1258 AAUAGCAGUUUACAACCAGAAUU 80 2300 AACAGAUACAGUAUGUAUACAUU 81 664 AAAGGCAUCCAUGAAUACGACUU 82 901 AAUGUCUCCAUAAUUCUGUUCUU 83 4301 AAAUACCAUAUGUCCUUAUCAUU 84 1900 AACGUAACGAGUGAAAUAGAAUU 85 2591 AAGUCCAAGGCUGGCGACAGCUU 86 2949 AAGUUCAUGGUAUCGUGCAUGUU 87 3821 AAUAUCACACAAGUGUCUUCAUU 88 957 AAUUGUGAGCAUCAAAGACUAUU 89 455 AAGGAAUGGUGGAAACAAGGGUU 90 2466 AAAUGUGUCCACGAAGUAGCUUU 91 1870 AAGCUAAUGCUGUUUACCGUGUU 92 1630 AACUUUAUGGUGACCUCCUAUUU 93 1679 AAGAAAUGGCAUUCUGUAGGUUU 94 827 AAGAUCGACUGACCAAUCGCCUU 95 873 AACAAUCGUCAAUAACCGGGUUU 96 1378 AAGAUUUGCUGUAAUGCAGGCUU 97 872 AAACAAUCGUCAAUAACCGGGUU 98 1683 AAUGGCAUUCUGUAGGUUUAUAG 99 1549 UAGGGAUGAGGUUAGGAAUAUUC 100 4253 GAUCGCCUUAAUACCAGAAAUGA 101 4683 AAGCCCAAACAUUUGUAACAAAC 102 1462 UAGGCAUAUUUCAGGCUUUAAAU 103 1656 AAGGGCUGUUAGAAGUUCUAUCU 104 541 GACCGGCGUCGAGAAUUUCAACU 105 4420 CAUCCGAUUAUGCCUUAUUUAUA 106 722 UAGGUGGUCAGAGAUCAGAAAGG 107 2597 AAGGCUGGCGACAGCUUGAAAAG 108 449 CAGCCCAAGGAAUGGUGGAAACA 109 4618 UAUGUCAUGAGAAGGCUAAAUAU 110 228 GAGCGGCAAGUCCACCUUCCUGA 111 3795 AAUGCCUUCUCAUUUAAUUCUGA 112 1865 AAGGCAAGCUAAUGCUGUUUACC 113 4682 AAAGCCCAAACAUUUGUAACAAA 114 1371 CAUCGCCAAGAUUUGCUGUAAUG 115 1655 UAAGGGCUGUUAGAAGUUCUAUC 116 509 UAUGGGCAGACAGCGGCAUACAG 117 2174 AACUCCACACUGUGCCAUUUGUG 118 811 GACCAGGUGCUUAUGGAAGAUCG 119 4673 CAUGCCUGUAAAGCCCAAACAUU 120 3069 AAUUGCAGUGCUAAUGAAUAUCG 121 3309 UACCACCAAGAAGUGUUGAAACA 122 3207 AAGAGGACACUUCAUCUUACUUA 123 124 GAGGCCGAGCAGCAACGCAAGUC 124 142 AAGUCCAAGGAGAUCGACAAAUG 125 1072 AAGCCCUUAUACCACCACUUCAC 126 1703 UAGAAGGUUUAGCCUUCAUAUUU 127 1845 CAGGUGGUAUGGGAGAGCAAAAG 128 4505 AACCCUCAAAUUGGUGCUUUCAU 129 4130 UAAGGUGUAUUGGCAUGUAAUUU 130 1682 AAAUGGCAUUCUGUAGGUUUAUA 131 2596 CAAGGCUGGCGACAGCUUGAAAA 132 355 GAUGCUCGAGAGAAGCUUCAUAU 133 2491 GAUCGCAGAUACAUUCAUAGUGA 134 3209 GAGGACACUUCAUCUUACUUAAG 135 3127 GAGAGUUUACCCAUACAUUUAGC 136 3318 GAAGUGUUGAAACACCAAAUAGA 137 3639 AAGGUGCUCAUAAUUUCACUAUG 138 4628 GAAGGCUAAAUAUCAGUGUUAAU 139 3063 UAGCAUAAUUGCAGUGCUAAUGA 140 2557 UAGGCUGUAUGUAGUGCUACAAU 141 3276 AAGCAGAAAUCACCAAGUUUCCC 142 2078 UAUCUCAGUUGGUCAGUAAAGAC 143 1529 AAGGUGUCCUUAAAUACUUGUAG 144 3794 GAAUGCCUUCUCAUUUAAUUCUG 145 971 AAGACUAUUUCCUAGAAUUUGAA

An antisense oligonucleotide may also be used to specifically reduce G protein expression, for example, by inhibiting transcription and/or translation. An antisense oligonucleotide is complementary to a sense nucleic acid encoding a G protein. For example, it may be complementary to the coding strand of a double-stranded cDNA molecule or complementary to an mRNA sequence. It may be complementary to an entire coding strand or to only a portion thereof. It may also be complementary to all or part of the noncoding region of a nucleic acid encoding a G protein. The non-coding region includes the 5′ and 3′ regions that flank the coding region, for example, the 5′ and 3′ untranslated sequences. An antisense oligonucleotide is generally at least six nucleotides in length, but may be about 8, 12, 15, 20, 25, 30, 35, 40, 45, or 50 nucleotides long. Longer oligonucleotides may also be used. An antisense oligonucleotide may be prepared using methods known in the art, for example, by expression from an expression vector encoding the antisense oligonucleotide or from an expression cassette. Alternatively, it may be prepared by chemical synthesis using naturally-occurring nucleotides, modified nucleotides or any combinations thereof. In some embodiments, the oligonucleotides are made from modified nucleotides or non-phosphodiester bonds, for example, that are designed to increase biological stability of the oligonucleotide or to increase intracellular stability of the duplex formed between the antisense oligonucleotide and the sense nucleic acid. Naturally-occurring nucleotides include the ribose or deoxyribose nucleotides adenosine, guanine, cytosine, thymine and uracil. Examples of modified nucleotides include 5-fluorouracil, 5-bromouracil, 5-chlorouracil, 5-iodouracil, hypoxanthine, xanthine, 4-acetylcytosine, 5-(carboxyhydroxylmethyl)uracil, 5-carboxymethylaminomethyl-2-thiouridine, 5-carboxymethylaminomethyluracil, dihydrouracil, beta-D-galactosylqueosine, inosine, N6-isopentenyladenine, 1-methylguanine, 1-methylinosine, 2,2-dimethylguanine, 2-methyladenine, 2-methylguanine, 3-methylcytosine, 5-methylcytosine, N6-adenine, 7-methylguanine, 5-methylaminomethyluracil, 5-methoxyaminomethyl-2-thiouracil, beta-D-mannosylqueosine, 5′-methoxycarboxymethyluracil, 5-methoxyuracil, 2-methylthio-N6-isopentenyladenine, uracil-5oxyacetic acid, wybutoxosine, pseudouracil, queosine, 2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil, 5-methyluracil, uracil-5-oxacetic acid methylester, uracil-5-oxacetic acid, 5-methyl-2-thiouracil, 3-(3-amino-3-N-2-carboxypropyl)uracil, (acp3)w, and 2,6-diaminopurine. Thus, oligonucleotides of the invention may include modified nucleotides, as well as natural nucleotides such as combinations of ribose and deoxyribose nucleotides, and an antisense oligonucleotide of the invention may be of any length discussed above and that is complementary SEQ ID NO: 1, 3 and 5.

An angiogenesis-modulating agent of the invention may also be a ribozyme. A ribozyme is an RNA molecule with catalytic activity and is capable of cleaving a single-stranded nucleic acid such as an mRNA that has a homologous region. See, for example, Cech, Science 236: 1532-1539 (1987); Cech, Ann. Rev. Biochem. 59:543-568 (1990); Cech, Curr. Opin. Struct. Biol. 2: 605-609 (1992); Couture and Stinchcomb, Trends Genet. 12: 510-515 (1996). A ribozyme may be used to catalytically cleave a G protein mRNA transcript and thereby inhibit translation of the mRNA. See, for example, Haseloff et al., U.S. Pat. No. 5,641,673. A ribozyme having specificity for a G protein nucleic acid may be designed based on the nucleotide sequence of SEQ ID NO: 1 and 2. Methods of designing and constructing a ribozyme that can cleave an RNA molecule in trans in a highly sequence specific manner have been developed and described in the art. See, for example, Haseloff et al., Nature 334:585-591 (1988). A ribozyme may be targeted to a specific RNA by engineering a discrete “hybridization” region into the ribozyme. The hybridization region contains a sequence complementary to the target RNA that enables the ribozyme to specifically hybridize with the target. See, for example, Gerlach et al., EP 321,201. The target sequence may be a segment of about 5, 6, 7, 8, 9, 10, 12, 15, 20, or 50 contiguous nucleotides selected from a nucleotide sequence having SEQ ID NO:1 or 2. Longer complementary sequences may be used to increase the affinity of the hybridization sequence for the target. The hybridizing and cleavage regions of the ribozyme can be integrally related; thus, upon hybridizing to the target RNA through the complementary regions, the catalytic region of the ribozyme can cleave the target. Thus, an existing ribozyme may be modified to target a G protein of the invention by modifying the hybridization region of the ribozyme to include a sequence that is complementary to the target G protein. Alternatively, an mRNA encoding a G protein may be used to select a catalytic RNA having a specific ribonuclease activity from a pool of RNA molecules. See, for example, Bartel & Szostak, Science 261:1411-1418 (1993).

An agent of the invention may also be an analogue of GDP and/or GTP. The analogue may be an activator or an inhibitor of G protein function. Non-limiting examples of a GDP and/or GTP analogue include 8-bromoguanosine 5′-triphosphate; 3,4-diaminobenzophenone(DABP)-phosphoramidate-GTP; guanosine-5′-O-(3-thiotriphosphate (GTP gamma S); GppNHp; GppCH2p; GDP-beta S; 8-aza-7-deazaguanine; 6-thioguanine; GMP-PNP; and 8-oxo-guanine.

Thus, agents of the invention include those that will reduce as well as enhance angiogenesis and may be an oligonucleotide, a G protein nucleic acid, and an activating or inhibitory GTP and/or GDP analogue. An oligonucleotide may reduce G protein expression and activity, while an inhibitory GDP and/or GTP analogue may reduce G protein function. Similarly, a G protein nucleic acid, e.g. one incorporated into an expression vector and operably-linked to an expression control sequence, may increase G protein expression and activity, while an activating GDP and/or GTP analogue such as GTP gamma S may increase G protein function.

Pharmaceutical Compositions

Agents of the invention may be incorporated into a pharmaceutical composition suitable for administration to a mammal. A pharmaceutical composition of the invention typically comprises the active agent and a pharmaceutically acceptable carrier. As used herein, the phrase “pharmaceutically acceptable carrier” means any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like known in the art to be compatible with pharmaceutical administration to a mammal. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the pharmaceutical composition of the invention is contemplated. In addition, supplementary active compounds may also be included into the pharmaceutical compositions.

A pharmaceutical composition of the invention is formulated to be compatible with the intended route of administration. Examples of routes of administration include parenteral, intravenous, intradermal, subcutaneous, oral, by inhalation, transdermal (topical), transmucosal, and rectal administration. Solutions or suspensions used for parenteral, intradermal or subcutaneous application may include (1) a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; (2) antibacterial agents such as benzyl alcohol or methyl parabens; (3) antoxidants such as ascorbic acid or sodium bisulfite; (4) chelating agents such as ethylenediaminetetraacetic acid; (5) buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. pH may be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation may be enclosed in ampoules, disposable syringes or multiple dose vials.

Pharmaceutical compositions suitable for injection include sterile aqueous solutions or dispersions and sterile powders for extemporaneous preparation of sterile injectable solutions or dispersions. For intravenous administration, suitable carriers include physiological saline, bacteriostatic water, or phosphate buffered saline. Compositions must be sterile and be stable under the conditions of manufacture and storage and must be preserved against contamination by microorganisms such as bacteria and fungi. The carrier may be a solvent or dispersion medium containing, for example, water, ethanol, polyol (e.g. glycerol, propylene glycol and liquid polyethylene glycol), and suitable mixtures thereof. The proper fluidity may be achieved, for example, by using a coating such as lecithin, by maintaining the required particle size in the case of dispersion and by using surfactants. Prevention of the action of microorganisms may be achieved using various antibacterial and antifungal agents such as, for example, parabens, chlorobutanol, phenol, ascorbic acid, and thimerosal. Other ingredients such as an isotonic agent or an agent that delays absorption (e.g. aluminum monostearate and gelatin) may be included.

Sterile injectable solutions may be prepared by incorporating the active agent in the required amount in an appropriate solvent with one or a combination of ingredients discussed above, as required, followed by filtered sterilization. Dispersions may be prepared by incorporating the active compound into a sterile vehicle that contains a basic dispersion medium and other required ingredients discussed above. In the case of sterile powders for the preparation of injectable solutions, the preferred methods of preparation include vacuum drying and freeze-drying which yield a powder of the active ingredient and any additional desired ingredient from a previously sterile-filtered solution.

Oral compositions may include an inert diluent or an edible carrier. They may be enclosed in gelatin capsules or compressed into tablets. For the purpose of oral therapeutic administration, the active compound may be incorporated with excipients and used in the form of tablets, troches, or capsules. Oral compositions may also be prepared using a fluid carrier. Pharmaceutically compatible binding agents and/or adjuvant materials may be included as part of the composition. The tablets, pills, capsules, troches and the like may contain any of the following ingredients or compound of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose; a disintegrating agent such as alginic acid or corn starch; a lubricant such as magnesium stearate; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin; or a flavoring agent such as peppermint, methyl salicylate or orange flavoring.

For administration by inhalation, the composition may be delivered in the form of an aerosol spray from a pressurized container or dispenser which contains a suitable propellant, for example, a gas such as carbon dioxide or a nebulizer.

Systemic administration may also be by transmucosal or transdermal means. For transmucosal or transdermal administration, penetrants known in the art to be appropriate to the barrier to be permeated may be used. These include detergents, bile salts and fusidic acid derivatives for transmucosal administrations, which may be accomplished using nasal sprays, for example. For transdermal administration, the active compounds are formulated into ointments, salves, gels or creams as generally known in the art.

In one embodiment, the agents of the invention may be prepared with carriers that will protect the agent against rapid elimination from the body, such as a controlled release formulation such as implants and microencapsulated delivery systems. Biodegradable biocompatible polymers may be used. These include ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. Liposomal suspensions, including those targeted to infected cells with monoclonal antibodies to viral antigens may also be used as pharmaceutically acceptable carriers. These may be prepared using methods known in the art.

Oral or parenteral compositions may be formulated in dosage unit form for ease of administration and uniformity of dosage. The phrase “dosage unit form” refers to physically discrete units suited as unitary dosages for the subject to be treated, each unit containing a predetermined quantity of active compound calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. The specification for the dosage unit forms is dependent on the unique characteristics of the active compound and the particular therapeutic effect to be achieved.

The oligonucleotides of the invention may be inserted into vectors and used as gene therapy vectors, which may be delivered to a subject by intravenous injection, local administration or by stereotactic injection. See, for example, U.S. Pat. No. 5,328,470 and Chen et al., PNAS 91:3054 (1994). The pharmaceutical preparation of the gene therapy vector may include the gene therapy vector in an acceptable diluent or may comprise a slow release matrix in which the gene delivery vehicle is imbedded. Thus, the oligonucleotide of the invention may be administered to a subject by direct injection at a tissue site or generated in situ. Alternatively, it may be modified to target selected cells and then administered systemically. For example, antisense molecules may be modified such that they bind to receptors or antigens expressed on a selected cell surface.

The pharmaceutical compositions may be included in a container, pack or dispenser together with instructions for administration. Therefore, the invention also provides an article of manufacture comprising a pharmaceutical composition of the invention and instructions for use of the composition for the treatment of conditions associated with excessive, insufficient or aberrant angiogenesis or for the treatment of conditions in which an increase or decrease of angiogenesis would have therapeutic effects. Conditions for which an agent of the invention would be useful are discussed in the following section.

The dosage to be administered to the mammal may be any amount appropriate to reduce or promote G protein expression. The dosage may be an effective dose or an appropriate fraction thereof. This will depend on individual patient parameters including age, physical condition, size, weight, the condition being treated, the severity of the condition, and any concurrent treatment. Factors that determine appropriate dosages are well known to those of ordinary skill in the art and may be addressed with routine experimentation. For example, determination of the physicochemical, toxicological and pharmacokinetic properties may be made using standard chemical and biological assays and through the use of mathematical modeling techniques known in the chemical, pharmacological and toxicological arts. The therapeutic utility and dosing regimen may be extrapolated from the results of such techniques and through the use of appropriate pharmacokinetic and/or pharmacodynamic models. The precise amount to be administered to a patient will be the responsibility of the attendant physician. However, that a patient may insist upon a lower dose or tolerable dose for medical reasons, psychological reasons or for virtually any other reasons.

Agents of the invention such as a GDP or GTP analogue may be administered orally or by injection at a dose of from 0.1 to 2000 mg/kg weight of the mammal, preferable from 1 to 200 mg/kg weight of the mammal. An oligonucleotide of the invention may be administered orally or by injection at a dose of from 0.05 to 500 mg per kg weight of the mammal, preferably 0.5 to 50 mg/kg weight of the mammal. The dose range for adult humans is generally from 4 to 40,000 mg/day and preferably 40 to 4,000 mg/day. As certain agents of the invention are long acting, it may be advantageous to administer an initial dose of 80 to 4,000 mg the first day then a lower dose of 20 to 1,000 mg on subsequent days.

Methods of Use

An agent or a pharmaceutical composition of the invention may be used to reduce or promote G protein expression and/or activity in a mammal. For example, an oligonucleotide may be used to reduce G protein expression and activity, while an inhibitory GDP or GTP analogue may be used to reduce G protein function. Similarly, a G protein nucleic acid, e.g. one incorporated into an expression vector and operably-linked to an expression control sequence, may be used to increase G protein expression and activity, while an activating GDP or GTP analogue such as GTP gamma S may be used to increase G protein function.

A mammal may be a mouse, a rabbit, a monkey, a cow, a pig, or a human. An agent or composition of the invention may be administered to a mammal exhibiting a disease or condition associated with G protein expression or a mammal at risk for developing such a condition.

The disease or condition may be one associated with excessive, insufficient or otherwise abnormal angiogenesis or a condition associated with angiogenesis such that the modulation of angiogenesis provides a therapeutic benefit. Non-limiting examples of such conditions include cancers such as melanoma, lymphoma, cancer of the lung, breast, colon, kidney, pancreas, bone, and brain, as well as cancer metastasis; infectious diseases such as Orf, HPV, HIV infections; autoimmune disorders such as systemic sclerosis, multiple sclerosis, Sjogren's disease; vascular malformations; transplant arteriopathy and atherosclerosis; obesity; skin disorders such as psoriasis, allergic dermatitis, Kaposi's sarcoma in AIDS patients and systemic sclerosis; eye diseases such as diabetic retinopathy; retinopathy of prematurity and persistent hyperplastic vitreous syndrome; gastrointestinal tract diseases such as inflammatory bowel disease, periodontal disease and liver cirrhosis; reproductive system diseases such as endometriosis and ovarian cysts or hyperstimulation; bone or joint diseases such as arthritis and synovitis and HIV-induced bone marrow angiogenesis; and kidney disease such as diabetic nephropathy. See, for example, Carmeliet, Nature 438: 932-936, Supplementary Table 1 (2005). Non-limiting examples of conditions related to insufficient angiogenesis include Alzheimer's disease; stroke; diabetes; hypertension; hair loss; preeclampsia; lupus; neonatal respiratory distress syndrome; ischemic heart disease, osteoporosis and nephropathy. See, for example, Carmeliet, Nature 438: 932-936; Supplementary Table 2 (2005). An agent of the invention may be used prophylactically, for example, administration may occur prior to the onset of symptoms related to the disease or condition. Alternatively, an agent or composition of the invention may be used to treat an existing condition, for example, to reduce or prevent growth of a tumor or cancer cell and/or prevent tumor metastasis. An agent or composition of the invention may be administered in an appropriate route as discussed earlier.

An oligonucleotide of the invention may also be used as an hybridization probe to determine the level of expression of a G protein in a sample. Methods of hybridization using oligonucleotides, for example, Northern hybridization or in situ hybridization, are known in the art.

Screening Methods

In one embodiment, the invention provides a method for screening for an anti-cancer, an anti-angiogenesis agent, or an agent that promotes angiogenesis. The anti-cancer or anti-angiogenesis agent or the agent that promotes angiogenesis may be a peptide, a peptidomimetic, a small molecule or the like that reduces or promotes the expression and/or activity of a G protein.

The screening method may be a cell-based assay in which a cell that expresses a G protein is contacted with a test compound, and the level of G protein expression is determined. G protein expression may be determined by examining the level of transcription or translation using methods known in the art. For example, the level of G protein transcript may be determined by Northern or in situ hybridization using an oligonucleotide that would hybridize to the G protein transcript under stringent condition. Stringent conditions refer to conditions for hybridization and washing under which nucleotide sequences at least 60%, for example 65%, 70%, 75% or more than 75% identical to each other typically remain hybridized to each other. Such stringent conditions are known to those skilled in the art and can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989). A preferred non-limiting example of stringent hybridization conditions are hybridization in 6× sodium chloride/sodium citrate (SSC) at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 50-65° C. Alternatively, the level of G protein translation may be determined using a G protein-specific antibody in methods known in the art such as Western hybridization or immuno-precipitation. The level of G protein expression in a cell that has been contacted with the test compound is compared to the level of G protein expression in a control cell that has not been contacted with the test compound. An anti-cancer or anti-angiogenesis agent is one that reduces expression of a G protein in the cell, while an angiogenesis promoting agent is one that increases expression of a G protein in a cell.

The screening method may also be a cell-free assay in which a purified or partially-purified preparation containing a G protein is contacted with a test compound, and then the activity of the G protein is determined. G protein activity assay is known in the art. See, for example, Jiang, et al., Nature 395: 808-813 (1998).

The screening method may also be an in vivo assay in which an animal injected with tumor cells is administered a test compound and then angiogenesis, tumor growth or the level of G protein expression or activity, is assessed using methods known in the art. See, e.g., Examples 1, 7, and 8 described herein. In each case, a test compound is an anti-angiogenesis or anti-cancer agent if it reduces G protein expression and/or activity or if it reduces tumor growth and/or angiogenesis.

In another aspect, the invention provides a method for screening for a compound that promotes angiogenesis. In methods for screening for a compound that promotes angiogenesis, similar cell-based, cell-free or in vivo assays such as those described above may be employed. A test compound that increase G protein expression and/or activity is one that promotes angiogenesis.

The invention will be further described in the following examples, which do not limit the scope of the invention described in the claims.

EXAMPLES Example 1 Materials and Methods

Plasmid Constructs: Wild-type and mutant genes encoding human Gα₁₂, Gα₁₃, and Rac cloned in pcDNA3.1 were obtained from Guthrie Research Center. Several Gα₁₃ C-terminal mutants were made. One C-terminal mutant was a truncated protein lacking the last five amino acid residues QLMLQ. A second C-terminal mutant was a similarly truncated protein fused to a Myc tag and a His₆ tag at its C-terminus (EQKLISGGDLNMHTEHHHHHH (SEQ ID NO: 5). This Myc/His₆ fusion protein was generated by subcloning and expression from a pcDNA3.1-myc-His vector. The third Gα₁₃ mutant had a TAP tag at the C-terminus. Rigaut et al., Nat Biotechnol 17: 1030-1032 (1999). The TAP tag has 184 amino acid residues including a calmodulin-binding peptide, a TEV cleavage site and two IgG binding domains of protein A. The Gα_(13/1)-DD1 chimera (in pET28a) was made based on the Gα_(13/i)-5 chimera (Chen et al., Nat Struct Mol Biol 12: 191-197 (2005)) with the following sequences: amino acid residues 1-47 of Gα_(i1)+64-235 of Gα₁₃+213-230 of Gα_(i1)+254-262 of Gα₁₃+240-353 of Gα_(i1). The GST-PBD plasmid was provided by Y. Zheng (Wu et al., Biochemistry 42: 1129-1139 (2003)). Sequences of the final constructs were verified by DNA sequencing.

Wound Healing Assay: Wild type and Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) MEF cells isolated from E8.0 Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) embryos (Gu et al., Proc Natl Acad Sci USA 99: 9352-9357 (2002)) in Dulbecco's Modified Eagle Medium (DMEM) (Invitrogen) containing 10% FBS were seeded into wells of 24-multiwell plates (Becton-Dickinson) (Shan et al., Proc Natl Acad Sci USA 102: 3772-3776 (2005); Yang and Huang, J Biol Chem 280: 27130-27137 (2005)). After they grew to confluency, wounds were made with sterile pipet tips. Cells were washed with Phosphate Buffered Saline (PBS) and refreshed with medium containing 10% fetal bovine serum (FBS) or 20 ng/mL platelet-derived growth factor (PDGF-BB). After overnight incubation at 37° C., cells were fixed and photographed. MEF cells were transfected with Lipofectamine-2000 (transfection efficiency was 10 to 30%) (Invitrogen).

Chamber Cell Migration Assay: Cell migration was assayed in Boyden chambers [8.0 μm pore size polyethylene terephthalate membrane, FALCON cell culture insert (Becton-Dickinson)] (Shan et al., Proc Natl Acad Sci USA 102: 3772-3776 (2005); Yang and Huang, J Biol Chem 280: 27130-27137 (2005)). Cells were first trypsinized and counted. Then 5-10×10⁴ cells in serum free medium (300 μL) were added to the upper chamber, and 500 μL of appropriate medium with 10% FBS or 20 ng/mL PDGF were added to the lower chamber. Transwells were incubated for 4-6 hours at 37° C. Cells on the inside of the transwell inserts were removed with a cotton swab, and cells on the underside of the insert were fixed and stained. Photographs of three random fields were taken, and the number of cells counted to determine the average number of cells that had transmigrated.

MAPK Assay: Whole cell lysates were prepared from MEF cells, Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, and Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₃ cells, with or without stimulation by PDGF. Activated ERK MAPK proteins were immunoprecipitated from cell lysates using a monoclonal antibody against phospho-p44/42 ERK MAPK (cross-linked to agarose beads) (Cell Signaling Technology). The ERK MAPK activity was measured by the phosphorylation of substrate GST-Elk-1 that was detected by western blotting with an anti-phospho-Elk-1 antibody.

RNA Interference: RNA interference was performed with Qiagen's 2-For-Silencing siRNA Duplexes. Cells were plated in 6-well plates the day before transfection. 2.5 μg siRNA were diluted in 100 μL buffer EC-R (Qiagen). 7.5 μL RNAiFect transfection reagent (Qiagen) were added to form complexes. After incubation for 15 minutes at room temperature, the complexes were added to the cells. Two days later, the cells were again transfected with the same amount of siRNA. Cells were assayed after three more days' incubation. The sequences for Gα₁₃ siRNA oligonucleotides were r(GUA CGA CUU UGA AAU UAA A)dTdT (SEQ ID NO: 6) for the sense strand and r(UUU AAU UUC AAA GUC GUA C)dTdC (SEQ ID NO: 7) for the antisense strand. The sequences for the second pair of oligonucleotides used in the interference assay (data not shown) were r(GGG UGA GUC UGU AAA GUA U)dTdT (SEQ ID NO: 8) for the sense strand and r(AUA CUU UAC AGA CUC ACC C)dAdG (SEQ ID NO: 9) for the antisense strand. The control siRNA oligonucleotides were supplied by Qiagen.

Rac Activation Assay: After stimulation with 20 ng/mL PDGF for 10 minutes, cells were washed with PBS and lysed with lysis buffer (20 mM Tris-HCl (pH 8.0), 150 mM NaCl, 1 mM EDTA, 1 mM EGTA, 1% Triton X-100, 1 μg/mL Leupeptin, 1 mM PMSF). 30 μg of GST-PBD attached to beads were added to cell lysates. After incubation at 4° C. for 60 minutes, the beads were washed three times with lysis buffer. SDS sample buffer was added to the beads, and the samples were boiled at 90° C. for 10 minutes and run on 12% SDS-PAGE gels. Immunodetection of Rac was done with anti-Rac antibody (clone 23A8, Upstate Biotechnology).

Fluorescence Microscopy: Staining and observation of actin stress fibers were performed as previously described (Lowry et al., Dev Cell 2: 733-744 (2002)). Cells were plated onto coverslips coated with gelatin. Cells were then fixed with 3.7% formaldehyde, and the fixed cells were then permeabilized in 0.1% Triton X-100 for 5 minutes. After washing in PBS, phalloidin conjugated to rhodamine (Molecular Probes) in a solution containing PBS and 1% BSA was added to stain actin. After incubation for 30 minutes at room temperature, the cells were washed extensively to reduce nonspecific interactions. The coverslips were fixed onto slides and imaged using a Zeiss fluorescence microscope. For Rac and cortactin staining, anti-Rac and anti-cortactin antibodies were from Upstate Cell Signaling Solutions. The immuno-staining was done as previously described (Lowry et al., Dev Cell 2: 733-744 (2002)).

Co-immunoprecipitation Assay: In vivo co-immunoprecipitation was done as described (Lowry et al., Dev Cell 2: 733-744 (2002)). Plasmid cDNAs were transfected into HEK293T cells using the calcium phosphate method, and whole cell extracts were made 48 hours later. 500 μL of whole cell extract in cell lysis buffer were pre-cleared with 20 μL of protein A/G agarose beads for 30 minutes at 4° C. Lysates were then incubated with monoclonal anti-Rac antibody (clone 23A8, Upstate) for 2 hours at 4° C. 40 μL of protein A/G agarose beads were then added. After overnight incubation, the beads were washed three times with 500 μL of lysis buffer. Samples were run on 10% SDS-PAGE gels and western blotted with polyclonal anti-Gα₁₃ antibody (A-20, Santa Cruz Biotechnology). For in vitro co-immunoprecipitation, cell extracts were replaced with purified proteins in PBS.

Protein Purification: GST or His₆-tagged Rac proteins were purified from E. coli, and recombinant Gα₁₃ was purified as a His₆-tagged protein from Sf9 cells as described (Lowry et al., Dev Cell 2: 733-744 (2002)). Gα_(i1) and Gα₁₃/_(i)-DD1 (in pET28a) proteins were purified from E. coli as His₆-tagged proteins.

Tumour Xenograft in a Murine Model: Studies using mice were performed in compliance with the Institutional Animal Care and Use Committee of Weill Medical College of Cornell University.

Gα₁₃ ^(+/−) mice and wild-type littermates were injected intradermally in the right lower back with ˜2×10⁶ mouse B16 melanoma cells or LLC lung tumor cells (ATCC). Tumour size was measured at the indicated dates with a Vernier caliper and calculated by the formula V=L×W²/2.

Immunohistochemistry: LLC tumors were excised 8 days after inoculation in wild type and Gα₁₃ ^(+/−) mice. Tissue samples were fixed in 4% paraformaldehyde and imbedded in O.C.T. Sections of 8 μm were prepared and stained with hematoxylin and eosin (H&E) for histopathological analyses, with anti-PECAM/CD31 antibody for blood vessels analyses, and anti-VEGFR2 antibody for the analyses of recruitment of endothelial precursors and endothelial cells.

Example 2 Role of Gα₁₃ in RTK-Induced Fibroblast Cell Migration

In wild-type MEF (mouse embryonic fibroblast) cells, addition of platelet-derived growth factor (PDGF-BB at 20 ng/mL) or serum (10% FBS) induced cell migration (FIG. 1A). Two approaches were used to study the migration of MEF cells, the qualitative wound-healing assay (FIGS. 1, A and B), the quantitative Boyden chamber assay (Shan et al., Proc Natl Acad Sci USA 102: 3772-3776 (2005); Yang and Huang, J Biol Chem 280: 27130-27137 (2005)) (FIGS. 1, C and D). For Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) MEF cells (MEF cells derived from the Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) mouse embryos), addition of PDGF did not induce cell migration (FIGS. 1, B and D). These Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells were capable of migrating since addition of serum induced their migration (FIGS. 1, B and D). Furthermore, activation of mitogen-activated protein kinase ERK by PDGF was not affected in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells (FIG. 1E). These results suggest that PDGF signaling to cell migration in fibroblast cells requires Gα₁₂ or Gα₁₃ or both. Similarly, epidermal growth factor (EGF) induced the migration of wild-type, but not Gα₁₂ ^(−/−)Gα₁₃ ^(−/−), MEF cells (FIG. 2).

To determine whether Gα₁₂ or Gα₁₃ or both are essential for PDGF-induced cell migration, wild-type Gα₁₂ or Gα₁₃ were re-expressed in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Cells stably re-expressing Gα₁₂ (Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₂ cells) did not respond to PDGF in terms of cell migration (FIGS. 1, F and H). On the other hand, cells stably re-expressing Gα₁₃ (Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₃ cells) showed PDGF-induced cell migration (FIGS. 1, G and I). Although Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells spread over a larger surface area and are thinner than wild-type MEF cells, this difference could not explain the defect in cell migration since Gα₁₂ ^(−/−)Gα₁₃ ^(−/−)+Gα₁₃ cells have the same morphology as Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Furthermore, Gα₁₃ ^(−/−) cells look similar to wild-type MEF cells (FIG. 3), and yet Gα₁₃ ^(−/−) cells did not migrate in response to PDGF or EGF. These data demonstrated that Gα₁₃ is essential for RTK-induced cell migration.

To further confirm the role of Gα₁₃ in growth factor-induced cell migration, two additional experimental systems were used. First, fibroblast cells isolated from Gα₁₃ single knockout mouse embryos were employed (FIG. 3A). While serum induced the migration of Gα₁₃ ^(−/−) cells, neither PDGF nor EGF could induce Gα₁₃ ^(−/−) cell migration. Re-expression of a wild-type Gα₁₃ in Gα₁₃ ^(−/−) cells rescued the migratory response to PDGF and EGF (FIG. 3A). The protein level of re-expressed Gα₁₃ was ˜80% that of endogenous Gα₁₃ protein (FIG. 3B). Second, RNA interference was used to down-regulate the endogenous Gα₁₃ protein levels in wild-type MEF cells. Transfection of an siRNA against mouse Gα₁₃ significantly reduced the level of endogenous mouse Gα₁₃ protein, while transfection with a control siRNA did not (FIG. 3C). The protein levels of Gα₁₂ and tubulin were not changed in these siRNA transfected cells (FIG. 3C). Notably, Gα₁₃ siRNA-treated cells showed a defective cell migratory response to PDGF stimulation as measured by both the chamber and wound-healing assays (FIGS. 3, D and E). Furthermore, a second siRNA against a different region of mouse Gα₁₃ gave similar results (data not shown). Moreover, human Gα₁₃ was expressed in siRNA-treated MEF cells. Introduction of human Gα₁₃ rescued PDGF-induced cell migration (FIG. 3D). Without PDGF (or other stimuli), migration of cells treated with Gα₁₃ RNAi or Gα₁₃ RNAi+human Gα₁₃ was not significantly different from that of cells treated with control RNAi (data not shown). Hence, these data confirmed that Gα₁₃ is essential for PDGF-induced MEF cell migration.

Example 3 Rac Acts Upstream of or in Parallel to Gα₁₃

To investigate the mechanism by which a heterotrimeric G protein, Gα₁₃, is involved in growth factor-induced cell migration, the relationship of Gα₁₃ was examined with other known signaling molecules downstream of PDGFRs. The Rho-family small GTPase Rac is involved in lamellipodia formation, cell adhesion, and cell migration (Hall, Science 279: 509-514 (1998); Ridley et al., Cell 70: 401-410 (1992); Sugihara et al., Oncogene 17: 3427-3433 (1998)). Genetic evidence has demonstrated that Rac is essential for PDGF-induced cell migration (Sugihara et al., Oncogene 17: 3427-3433 (1998)). As shown in FIG. 4A, dominant negative Rac mutants (Rac1 T17N) reduced PDGF-induced migration of MEF cells. Constitutively-active Rac mutants (Rac1 G12V) induced MEF cell migration in the absence of PDGF (FIG. 4B). These data confirm a role for Rac in PDGF-induced migration of MEF cells. Since both Gα₁₃ and Rac are involved in PDGF signaling to cell migration, studies were conducted to determine whether Rac acts upstream or downstream of G₁₃. Expression of the constitutively active Rac mutants (Rac1 G12V) failed to induce the migration of Gα₁₂ ^(−/−) Gα₁₃ ^(−/−) cells (FIGS. 4, C and D). Furthermore, in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, PDGF still activated Rac (FIG. 4E). Moreover, constitutively active mutant Gα₁₃Q226L could not induce MEF cell migration by itself, indicating that Gα₁₃ is required, but not sufficient, for cell migration (FIG. 4B). Therefore, Rac acts upstream of or in parallel to Gα₁₃ in PDGF-induced cell migration. If Rac works upstream of Gα₁₃, it is likely that Rac employs several signaling pathways to promote cell migration and that G₁₃ is part of one of these pathways.

Example 4 No Requirement for Coupling to a GPCR

If Rac works upstream of Gα₁₃, it is possible that PDGF, through Rac, induces the production and secretion of a ligand(s) that signals through a G₁₃-coupled GPCR (FIG. 5A). Alternatively, Rac could signal through Gα₁₃ without a GPCR (FIG. 5A). The possibility of a GPCR working between PDGFR and G₁₃ was tested. If there is a Gα₁₃-coupled receptor involved, a Gα₁₃ mutant that is defective in coupling to the receptor should not be able to rescue the Gα₁₃ deficiency. The C-termini of Gα subunits of heterotrimeric G proteins are essential for coupling to GPCRs (Bourne, Curr Opin Cell Biol 9: 134-142 (1997); Conklin et al., Nature 363: 274-276 (1993); Garcia et al., Embo J 14: 4460-4469 (1995); Gilchrist et al., J Biol Chem 276: 25672-25679 (2001); Hirsch et al., Genes Dev 5: 467-474 (1991); Kallal and Kurjan, Mol Cell Biol 17: 2897-2907 (1997); Masters et al., Science 241: 448-451 (1988); Onrust et al., Science 275: 381-384 (1997); Osawa and Weiss, J Biol Chem 270: 31052-31058 (1995); Sullivan et al., Nature 330: 758-760 (1987)). Addition of epitope tags at, or deletion of amino acid residues from, the C-terminal end of Go: blocks the GPCR-G protein interactions in vitro and in cells (Bourne, Curr Opin Cell Biol 9: 134-142 (1997) (and our unpublished observations). Several C-terminal tagged or truncated Gα₁₃ mutants were made that are defective in coupling to GPCRs, as described in Example 1. Since the results from these Gα₁₃ mutants were the same, only results from the Gα₁₃ mutant with deletion of the last five amino acid residues and with a C-terminal Myc and His₆ tags (referred to as the Gα₁₃ truncated mutant) are described in detail here. To confirm that this Gα₁₃ truncated mutant could not couple to a GPCR in cells, the formation of actin stress fibers induced by Gα₁₃-coupled receptors for lysophosphatidic acid (LPA) was examined. It was previously demonstrated that LPA uses Gα₁₃ to induce the formation of actin stress fibers in MEF cells (Gohla et al., J Biol Chem 274: 17901-17907 (1999)). As shown in FIG. 5B, while LPA induced formation of actin stress fibers in MEF cells, LPA failed to induce actin stress fiber formation in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Stable expression of wild-type Gα₁₃ in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells rescued the LPA-induced stress fiber formation. On the other hand, Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells stably expressing the Gα₁₃ truncated mutant did not show stress fiber formation after LPA stimulation (FIG. 5B). The protein expression levels of wild-type Gα₁₃ and the C-terminal truncated Gα₁₃ mutant proteins in these cells were similar, and ˜25% that of endogenous Gα₁₃ protein (FIG. 5C). These results confirm that a C-terminal truncated Gα₁₃ could not couple to GPCRs in cells. The rescue of PDGF-induced cell migration of Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells by wild-type and C-terminal truncated Gα₁₃ was studied. Both wild type Gα₁₃ and the C-terminal truncated Gα₁₃ rescued the cell migration defect of Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells (compare FIGS. 1 G & I with FIGS. 5 D & E). These results were verified by chamber assay showing a similar extent of rescue (FIGS. 1I and 5E). Furthermore, this bypass of a GPCR was not due to overexpression of Gα₁₃ mutant proteins in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells since the expression level of Gα₁₃ in Gα₁₃-deficient cells was less than that in wild-type MEF cells (FIG. 5C). Therefore, these data suggest that a G₁₃-coupled GPCR is unlikely to be essential in this pathway.

To further confirm this GPCR-independence, these experiments were repeated in Gα₁₃ ^(−/−) single knockout MEF cells and similar results were observed (FIG. 3A and FIG. 6). While expression of wild-type Gα₁₃ in Gα₁₃ ^(−/−) cells rescued LPA-induced stress fiber formation, the C-terminal truncated Gα₁₃ did not (FIG. 6). On the other hand, expression of either wild-type or the C-terminal truncated Gα₁₃ in Gα₁₃ ^(−/−) cells rescued PDGF- (and EGF) induced migration of these cells (FIG. 3A). Moreover, while wild-type Gα₁₃ rescued the migration defect of Gα₁₃ ^(−/−) cells in response to LPA, the C-terminal truncated Gα₁₃ mutant did not (FIG. 5F), reaffirming the functional uncoupling of this C-terminal truncated Gα₁₃ mutant from GPCRs. Together, these results demonstrate that coupling to GPCRs is not essential for the participation of Gα₁₃ in RTK-induced cell migration.

Example 5 Complex Formation Between Rac and Gα₁₃

To further understand the mechanism by which Rac and Gα₁₃ work together in RTK-induced cell migration, the possibility of Rac and Gα₁₃ existing in a complex was examined. First, in vitro binding experiments were performed using purified Rac1 and purified Gα₁₃ (FIG. 7, A-D). Since purified wild-type Gα₁₃ proteins were difficult to load with GTPγS, a Gα₁₃ and Gα_(i1) chimera (Gα₁₃/i-DD1) was generated based on the recently reported strategy (Chen et al., Nat Struct Mol Biol 12: 191-197 (2005)) (FIG. 7A). The Gα₁₃/i-DD1 protein could be purified from E. coli and the purified protein could be loaded with ³⁵S-GTPγS (the final ratio of ³⁵S-GTPγS loaded versus Gα₁₃/i-DD1 protein was ˜0.35). Gα₁₃/i-DD1, but not Gail, could rescue PDGF-induced migration of Gα₁₃ ^(−/−) cells (data not shown). Purified GST-Rac1 proteins pre-loaded with GDP or GTPγS were used for in vitro pull-down assays (FIG. 7B). When the binding reaction was carried out in the presence of 500 mM NaCl, only GST-Rac1(GTPγS) pulled down Gα₁₃/i-DD1(GDP) (FIG. 7B). When the binding experiments were performed under less stringent conditions (in the presence of 150 mM NaCl), additional weak interactions were observed between Rac1(GDP) and Gα₁₃/i-DD1(GDP), Rac1(GDP) and Gα₁₃/i-DD1(GTPγS), as well as Rac1(GTPγS) and Gα₁₃/i-DD1(GTPγS) (FIG. 7B). Furthermore, neither Rac1(GDP) nor Rac1(GTPγS) interacted with Gα_(i1)(GDP) or Gα_(i1)(GTPγS) (FIG. 7B). Moreover, RhoA(GDP) and RhoA(GTPγS) did not bind Gα₁₃/i-DD1 pre-loaded with GDP or GTPγS (FIG. 7B). Therefore, the strongest interaction is between Rac(GTPγS) and Gα₁₃(GDP). This result was confirmed with purified wild-type Gα₁₃ (FIG. 7C). When purified Rac1(GTPγS) and Gα₁₃(GDP) were incubated together, an anti-Rac antibody pulled-down Gα₁₃, while RhoA(GTPγS) did not under the same conditions (FIG. 7C). Similarly, anti-Gα₁₃ antibodies pulled down Rac1 only in the presence of Gα₁₃, reaffirming their direct interaction (data not shown). Since Gα₁₃(GDP) can bind Gβγ subunits, whether Rac(GTPγS) and Gβγ compete for binding to Gα₁₃(GDP) was examined. As shown in FIG. 7D, anti-Rac antibodies co-immunoprecipitated Gβγ only in the presence of Gα₁₃(GDP). These data imply that, after activation, Rac could interact with Gα₁₃ subunits or with Gα₁₃-Gβγ trimer. Together, these results demonstrate that Rae and Gα₁₃ directly interact with each other. Moreover, this provides an example of direct interaction between a heterotrimeric G protein and a Rho-family small GTPase.

Next, the interaction of Rae and Gα₁₃ in cells was investigated. First, the GDP or GTP dependency of the interaction in cells was examined. Constitutively active Rac1(G12V), wild-type Rac, constitutively active Gα₁₃(Q226L), and wild-type Gα₁₃ plasmids were used to transfect HEK293T cells. Cells were treated with or without PDGF. After immunoprecipitation with anti-Rac antibodies, co-precipitation of Gα₁₃ was examined with anti-Gα₁₃ antibodies (FIG. 7E). When Rac is active [Rac1(G12V)], co-immunoprecipitation of Gα₁₃ was detected in the absence of PDGF treatment (FIG. 7E, lane 1). This confirmed the in vitro data showing the interaction of Rac(GTPγS) and Gα₁₃(GDP). On the other hand, when wild-type Rac and Gα₁₃ were used, PDGF stimulation was required to observe the interaction (FIG. 7E, lanes 3 and 4). This PDGF treatment was likely needed to activate Rac, not Gα₁₃ since expression of Gα₁₃(Q226L) and wild-type Rac did not lead to co-immunoprecipitation without PDGF stimulation (FIG. 7E, lane 5). The interaction seen after PDGF treatment (FIG. 7E, lane 6) in cells expressing Rae and Gα₁₃(Q226L) might reflect the binding of activated Rac with endogenous Gα₁₃ or Gα₁₃(Q226L) after some of the Gα₁₃(Q226L) protein slowly hydrolyzed bound GTP. Indeed, co-immunoprecipitation of endogenous Rac and Gα₁₃ could be observed after PDGF stimulation (FIG. 7F). Hence, these data demonstrate that Rac and Gα₁₃ form a complex in cells.

Example 6 Deficiency of Gα₁₃ Blocks PDGF-Induced Membrane Ruffling and Lamellipodia Formation

Next the physiological consequence of the Rac and Gα₁₃ interaction was examined. First, testes were performed to examine whether purified Rac1 or Gα₁₃ proteins could affect each other's guanine nucleotide exchange or GTPase activity. No significant changes in these activities were examined. Second, the subcellular localization of Rac in the presence or absence of Gα₁₃ was examined. In wild-type MEF cells, PDGF treatment induced Rac translocation to membrane ruffles and lamellipodia at the cell periphery (80-90% of the cells) (FIG. 8A). Membrane ruffles and lamellipodia are protruding membrane structures at the cell edge that are essential for cell migration (Hall, Science 279: 509-514 (1998)). Strikingly, Rac was localized away from the peripheral membrane edge in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells after PDGF treatment (FIG. 8A). Instead, Rac was localized on the dorsal (top) surface of the cells forming a ring structure (called dorsal ruffles) (in ˜90% of the cells) (FIG. 8A). To confirm this altered Rac localization in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, the subcellular localization of cortactin was determined. Cortactin is a cytoplasmic protein that is recruited by activated Rac to membrane ruffles and lamellipodia, where cortactin stimulates Arp2/3-mediated actin polymerization (Weed et al., J Cell Sci 111 (Pt 16): 2433-2443 (1998)). As shown in FIG. 8B, in MEF cells PDGF stimulation translocated cortactin from the cytosol to membrane ruffles and lamellipodia; whereas in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells, cortactin was localized in the dorsal ruffles after PDGF addition. The cortactin staining patterns were similar to those of Rac, consistent with the altered subcellular localization of Rac in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells. Furthermore, the localization of F-actin polymers was studied (FIG. 8C). Similar to the localization of Rac and cortactin, F-actin polymers were also found in membrane ruffles and lamellipodia in MEF cells and in dorsal ruffles in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells (FIG. 8C). Since Rac mediates the PDGF-induced formation of both dorsal ruffles and lamellipodia (Buccione et al., Nat Rev Mol Cell Biol 5: 647-657 (2004)), the accumulation of dorsal ruffles in Gα₁₂ ^(−/−)Gα₁₃ ^(−/−) cells could be explained if Gα₁₃ were required for breaking down dorsal ruffles so that actin and other components could be recycled to form lamellipodia. If that were the case, it would provide a mechanism by which Gα₁₃ regulates PDGF-induced cell migration.

Example 7 Role of Gα₁₃ in Tumor Angiogenesis

To investigate the role of Gα₁₃ in RTK-induced migration of other cell types, endothelial cell migration induced by VEGF was examined. As shown in FIG. 9A, treatment of mouse endothelial cells (SVEC4-10 cells) with Gα₁₃ siRNA reduced the endogenous mouse Gα₁₃ protein level, but had no effect on the protein levels of Gα₁₂ and tubulin. This treatment also reduced VEGF-induced endothelial cell migration (FIG. 9B). A control siRNA had no effect on the Gα₁₃ protein level or cell migration (FIGS. 9, A and B). Re-expression of the human Gα₁₃ gene in these Gα₁₃ siRNA transfected cells restored the migratory response to VEGF (FIGS. 9, A and B). These data show that Gα₁₃ is also involved in VEGF-induced endothelial cell migration.

Next, to investigate the role of Gα₁₃ in RTK signaling in an animal model, tumor angiogenesis using a tumor xenograft mouse model was employed. Several RTKs including VEGF, PDGF, and angiopoietins play critical roles in developmental angiogenesis as well as in tumor angiogenesis (Risau, Nature 386: 671-674 (1997); Yancopoulos et al., Nature 407: 242-248 (2000)). Following a similar strategy used by Lyden et al., Nature 401: 670-677 (1999), the Gα₁₃ heterozygous knockout mouse was examined for their ability to support the growth of tumor xenografts. In these studies, mouse melanoma B16 tumor cells (FIG. 9C) or Lewis lung carcinoma (LLC) cells (FIG. 9D) were intradermally injected into host mice. Since Gα₁₃ ^(−/−) mouse embryos died at ˜E9.5, Gα₁₃ ^(+/−) mice were used as host mice. The hypothesis was that mice with reduced Gα₁₃ gene dosages might not be able to support neo-angiogenesis of xenografted tumors as in the case of Id genes (Lyden et al., Nature 401: 670-677 (1999)). Although Id1^(+/−) and Id1^(+/−)Id3^(−/−) mice were indistinguishable from the wild-type mice, neither of these heterozygous mice could support the neo-vascularization of xenografted tumors (Lyden et al., Nature 401: 670-677 (1999)). Melanoma B16 tumor cells or LLC tumor cells were intradermally injected into Gα₁₃ ^(+/−) mice and wild-type littermates. Wild-type mice had a rapid increase in tumor mass and died at 21±4 days (mean±s.d.) (FIG. 9C) or at 26±2 days (FIG. 9D). Significantly, the implanted tumors failed to grow on Gα₁₃ ^(+/−) mice (FIGS. 9 C and D). Moreover, all Gα₁₃ ^(+/−) mice remained healthy for more than 300 days until they were euthanized. These data demonstrate that reduced Gα₁₃ dosage inhibits tumor growth.

To obtain supportive evidence for the failed tumor angiogenesis in Gα₁₃ ^(+/−) host mice, histological analysis and immunohistochemistry were performed. LLC tumor tissues were removed 8 days after inoculation from some wild-type and Gα₁₃ ^(+/−) host mice, sectioned and stained with hematoxylin and eosin (FIG. 9E), with anti-PECAM/CD31 antibody (FIG. 9F), or with anti-VEGFR2 antibody (FIG. 9G). There were profound differences in the number of endothelial cells and of blood vessels in the tumor tissues from wild-type and Gα₁₃ ^(+/−) host mice. In wild-type host mice, tumors showed plenty of well-defined large vessels (FIG. 9F, two left panels), whereas in Gα₁₃ ^(+/−) mice, the tumors showed far less and stunted, occluded vessels (FIG. 9F, two right panels). Tumors from wild-type host mice showed intense staining with anti-VEGFR2 antibody, while tumors from Gα₁₃ ^(+/−) host mice showed few cells stained with VEGFR2, indicating a possible defect in the recruitment of endothelial progenitor cells and/or endothelial cells into the tumors in Gα₁₃ ^(+/−) host mice (FIG. 9G). This impaired recruitment could lead to few blood vessels in the tumors from Gα₁₃ ^(+/−) host mice, which in turn could account for defective tumor angiogenesis and tumor growth in Gα₁₃ ^(+/−) host mice. Hence, these data clearly showed a defect in tumor angiogenesis in Gα₁₃ ^(+/−) host mice.

Example 8 Role of Gα₁₂ in Tumor Growth

Lewis lung carcinoma (LLC) cells (2×10⁶ cells/mouse) were intradermally injected into wild-type (Gα₁₂ ^(+/+)) or Gα₁₂ ^(−/−) mice. While tumors grew rapidly in wild-type mice, they failed to grow significantly in Gα₁₂ ^(−/−) mice (FIG. 10). All wild-type mice died before Day 27. All Gα₁₂ ^(−/−) mice remained alive for more than 300 days until they were euthanized.

OTHER EMBODIMENTS

All patents and publications referenced or mentioned herein are indicative of the levels of skill of those skilled in the art to which the invention pertains, and each such referenced patent or publication is hereby incorporated by reference to the same extent as if it had been incorporated by reference in its entirety individually or set forth herein in its entirety. Applicants reserve the right to physically incorporate into this specification any and all materials and information from any such cited patents or publications.

The specific methods and compositions described herein are representative of preferred embodiments and are exemplary and not intended as limitations on the scope of the invention. Other objects, aspects, and embodiments will occur to those skilled in the art upon consideration of this specification, and are encompassed within the spirit of the invention as defined by the scope of the claims. It will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, or limitation or limitations, which is not specifically disclosed herein as essential. The methods and processes illustratively described herein suitably may be practiced in differing orders of steps, and that they are not necessarily restricted to the orders of steps indicated herein or in the claims. As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “an antibody” includes a plurality (for example, a solution of antibodies or a series of antibody preparations) of such antibodies, and so forth. Under no circumstances may the patent be interpreted to be limited to the specific examples or embodiments or methods specifically disclosed herein. Under no circumstances may the patent be interpreted to be limited by any statement made by any Examiner or any other official or employee of the Patent and Trademark Office unless such statement is specifically and without qualification or reservation expressly adopted in a responsive writing by Applicants.

The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intent in the use of such terms and expressions to exclude any equivalent of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention as claimed. Thus, it will be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Other embodiments are within the following claims. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group. 

1. A method for inhibiting angiogenesis in a mammal, the method comprising inhibiting the expression and/or activity of Gα₁₃ in the mammal by administering a guanine diphosphate or guanine triphosphate analogue selected from the group consisting of GDP beta S, GppNHp, and GppCH2p, with a small interfering RNA capable of hybridizing to a nucleic acid encoding a Gα₁₃ polypeptide under intracellular conditions and reducing expression of the Gα₁₃ protein in a cell, or any combination thereof in an amount effective to decrease expression and/or activity of the Gα₁₃ polypeptide.
 2. The method of claim 1, wherein the small interfering RNA has a sequence selected from the group consisting of SEQ ID NO: 6-9 and 69-145.
 3. The method of claim 1, wherein the mammal has cancer.
 4. The method of claim 1, wherein the small interfering RNA, analogue or any combination thereof is administered by direct injection to a localized area.
 5. The method of claim 1, wherein the expression and/or activity of Gα₁₂ or Gα₁₃ is decreased by about 20% to about 90%.
 6. The method of claim 1 wherein the expression and/or activity of Gα₁₂ or Gα₁₃ is decreased by about 30% to about 70%.
 7. The method of claim 1, wherein the method further comprises inhibiting endothelial cell migration.
 8. A method for inhibiting angiogenesis in a mammal, the method comprising inhibiting the expression and/or activity of Gα₁₃ in the mammal by administering a small interfering RNA having a sequence selected from the group consisting of SEQ ID NO: 6-9 and 69-145, or a complement thereof.
 9. The method of claim 8, further comprising administering a small interfering RNA having a sequence selected from the group consisting SEQ ID NO: 11-68.
 10. A method for inhibiting angiogenesis in a mammal, the method comprising administering an antibody and a small interfering RNA having a sequence selected from the group consisting of SEQ ID NO: 6-9 and 69-145.
 11. The method of claim 10, wherein the antibody reduces angiogenesis.
 12. The method of claim 10, wherein the antibody binds to the Gα₁₃ polypeptide. 